1. Field of the Invention
The present invention relates to a frequency synthesizer, and more specifically, to a low voltage frequency synthesizer using a boosting method for a power supply voltage of a charge pump, in which a dynamic range of the charge pump is extended to improve performance.
2. Discussion of Related Art
Recently, as convergence of technology necessitates integration, complementary metal-oxide semiconductor (CMOS) process techniques are rapidly developing. However, in analog circuit design, providing low voltage and low output impedance with the development of the CMOS process techniques is being raised as a problem to be overcome. In the structure of a frequency synthesizer requiring a low voltage and high performance, design for a charge pump serving as an analog circuit is considered an issue to be overcome. When designing the charge pump with a low voltage, the dynamic range of an output control voltage decreases. This may cause a reduction in frequency tuning range of a voltage-controlled oscillator (VCO), degradation of phase noise, and a reduction in design margin for performance drift compensation for an external environment and process variations.
In a conventional structure, a voltage higher than a supply voltage is generated through an additional circuit such as a Dixon charge pump, an AC amplifier, or a voltage doubler, and then used as a control voltage of a VCO or applied as a supply voltage of a charge pump.
Specifically, the Dixon charge pump is used as a charge transfer pump to convert an output voltage of the charge pump into a wide control voltage, and then apply the converted control voltage to the VCO, thereby improving locking range and phase noise characteristics. Alternatively, a boosting voltage generated through the voltage doubler or AC amplifier is applied as a supply voltage of the charge pump to improve locking range and phase noise characteristics.
However, the conventional structure wastes power, and a chip area increases because of the additional circuit.